Add 'direct' keyword to descendants option to query direct children (ep1)

-added 'direct' keyword also to Fetch Descendants Option along with 'all' and 'none' to Query direct child.
-added unit tests to test direct keyword

Issue-ID:CPS-1784
Change-Id: Iab7f59fbeebb03703626132c6d5c2afde0e5ab4d
Signed-off-by: Rudrangi Anupriya <ra00745022@techmahindra.com>
13 files changed